1. Field of the Invention
This invention relates to an X-ray projection exposure apparatus used in the manufacture of semiconductor integrated circuits.
2. Description of the Related Art
In solid-state devices, such as LSIs (large-scale integrated circuits) and the like, circuit patterns are becoming finer in order to increase the degree of integration and the operation speed thereof. In order to form such fine circuit patterns, reduction projection apparatuses having vacuum-ultraviolet exposure light sources are widely used. The resolution of such a reduction projection exposure apparatus depends on the exposure wavelength xcex and the numerical aperture NA of the projection optical system. In conventional exposure apparatuses, an approach of increasing the numerical aperture NA is adopted in order to improve the resolution.
However, this approach is now close to the limit of the use because of the resulting reduction in the depth of focus and difficulty in the design and the manufacturing of the dioptric system. Accordingly, an attempt to shorten the exposure wavelength xcex is being made. For example, light used for exposure shifts from the g-line (xcex=435.8 nm) to the i-line (xcex=365 nm) of the mercury lamp, and further to KrF excimer lasers (xcex=258 nm).
Although the resolution of the apparatus is improved by shortening the exposure wavelength, there is a theoretical limit on the resolution from the wavelength of ultraviolet rays used for exposure. Accordingly, in the extended technique of conventional exposure apparatuses using light, it is difficult to obtain a resolution equal to or less than 0.1 um.
Against such a technical background, X-ray reduction projection exposure apparatuses using vacuum-ultraviolet rays or soft X-rays (these two kinds of rays are hereinafter termed xe2x80x9cX-raysxe2x80x9d) as exposure light are attracting notice.
It is an object of the present invention to provide a practical X-ray projection exposure apparatus in which the above-described problems are solved.
It is another object of the present invention to provide a device manufacturing method having a high productivity using such an exposure apparatus.
According to one aspect, the present invention provides an X-ray projection exposure apparatus comprising a mask chuck for holding a reflection X-ray mask having a mask pattern thereon, a wafer chuck for holding a wafer onto which the mask pattern is transferred, an X-ray illuminating system for illuminating the reflection X-ray mask, held by the mask chuck, with X-rays, and an X-ray projection optical system for projecting the mask pattern of the reflection X-ray mask onto the wafer held by the wafer chuck with a predetermined magnification. The mask chuck comprises a mechanism for generating static electricity for attracting and holding the reflection X-ray mask by an electrostatic force.
It is preferable that the apparatus further comprises a detection mechanism for detecting an attracting force when attracting and holding the mask on the mask chuck. For example, the detection mechanism comprises a pressure sensor provided on an attracting surface of the mask chuck. It is preferable that the apparatus further comprises means for performing scanning exposure by moving both of the mask chuck and the wafer chuck. For example, the mask chuck holds the mask against gravity.
It is preferable that the apparatus further comprises means for changing the electrostatic force for attracting the mask by the mask chuck in accordance with the movement of the mask chuck. It is preferable that the relationship of {(the mass of the mask)xc3x97(acceleration due to gravity+the maximum acceleration of the mask while being moved)/(the maximum coefficient of static friction between the mask and the mask chuck)}xc3x97(safety factor) less than (the attracting force of the mask) is satisfied.
It is preferable that a plurality of projections are formed on a mask holding surface of the mask chuck, and the reflection X-ray mask is supported by the plurality of projections. The ratio of the area of contact between the distal ends of the projections and the mask to the entire area of the mask is equal to or less than 10%. It is preferable that the apparatus further comprises means for supplying voids formed between the projections with a cooling gas when the mask is supported on the projections. It is also preferable that the apparatus further comprises a temperature control mechanism for controlling the temperature of the mask chuck. For example, the temperature control mechanism comprises means for supplying the inside of the mask chuck with a temperature controlled medium, and a temperature sensor for detecting the temperature of the mask chuck. It is preferable that the mask chuck comprises a ceramic material or a glass material. It is also preferable that the apparatus further comprises a grounded earth pawl provided at at least a side of the mask chuck for supporting the mask.
For example, the reflection X-ray mask has a structure in which the mask pattern, made of an absorbing member, is formed on an X-ray reflecting multilayer film. For example, the X-ray illuminating system comprises a radiation source and a reflecting mirror. For example, the X-ray projection optical system comprises a reduction projection optical system having a plurality of X-ray-reflecting mirrors.
According to another aspect, the present invention provides a device manufacturing method comprising the step of transferring a mask pattern onto a wafer using the X-ray projection exposure apparatus having the above-described configuration.
According to still another aspect, the present invention relates to a device manufacturing method using an X-ray projection exposure apparatus comprising a mask chuck, a wafer chuck, an X-ray illuminating system, and an X-ray projection optical system. The mask chuck holds a reflection X-ray mask having a mask pattern thereon. The wafer chuck holds the wafer onto which the mask pattern is transferred. The X-ray illuminating system illuminates the reflection X-ray mask, held on the mask chuck, with X-rays. The X-ray projection exposure system projects the mask pattern of the reflection X-ray mask onto the wafer held by the wafer chuck with a predetermined magnification. The mask chuck comprises a mechanism for generating static electricity for attracting and holding the reflection X-ray mask by an electrostatic force. The method comprises the steps of generating static electricity with the mechanism of the mask chuck to hold the reflection X-ray mask with the mask chuck by an electrostatic force, holding the wafer with the wafer chuck, illuminating the reflection X-ray mask with X-rays using the X-ray illuminating system, and projecting the mask pattern of the reflection X-ray mask onto the wafer held by the wafer chuck with a predetermined magnification with the X-ray projection optical system to transfer the mask pattern onto the wafer.
The foregoing and other objects, advantages and features of the present invention will become more apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.